There is conventionally known an image forming apparatus that forms images on both sides of a sheet. In such conventional apparatus, an image is formed on one side of the sheet at an image forming unit, and the sheet is discharged from the image forming unit. Then, the sheet is reconveyed to the image forming unit to form an image on the other side of the sheet.
In such a type of image forming apparatus that forms images on both sides of a sheet, the image forming unit forms an image on a sheet while conveying the sheet with a drive force from a motor rotating in a normal direction. Further, the image forming apparatus includes a switchback roller and a reconveying roller. The switchback roller conveys the sheet discharged from the image forming unit toward a discharge tray with the drive force from the motor rotating in the normal direction. The switchback roller also reconveys the sheet toward the image forming unit with a drive force from the motor rotating in a reverse direction. The reconveying roller reconveys the sheet toward the image forming unit regardless of the rotating direction of the motor. Rotating direction of the reconveying roller is unchanged regardless of the rotating direction of the motor.
There is conventionally known a transmission mechanism for transmitting a drive force of a motor to a roller, such as the reconveying roller, in order to rotate the roller in a constant rotational direction irrespective of a rotating direction of the motor. Such a transmission mechanism is disclosed in Japanese Patent No. 4683058. The following reference numerals are those allotted in the description of the Japanese Patent.
According to an image forming apparatus disclosed in the Japanese Patent, a motor 84, idle gears 91, 93, 95, 96 and a swinging gear 92 are provided. The idle gear 91 is rotationally driven by the motor 84. The swinging gear 92 is swingably moved about a rotation axis of the idle gear 91 while meshing with the idle gear 91. The swinging gear 92 is swingably moved downward to be separated from the idle gear 95 and to mesh with the idle gear 93 when the motor 84 is rotated in a normal direction. The swinging gear 92 is swingably moved upward to be separated from the idle gear 93 and to mesh with the idle gear 95 when the motor 84 is rotated in a reverse direction.
The idle gear 93 capable of meshing with the swinging gear 92 during normal rotation of the motor 84 meshes with a cleaner drive gear 94 for driving a cleaning roller 41 through a plurality of idle gears. The cleaning roller 41 is rotated in a predetermined direction when the motor 84 is rotated in the normal direction.
Further, the idle gear 95 capable of meshing with the swinging gear 92 during reverse rotation of the motor 84 meshes with the cleaner drive gear 94 through the idle gear 96. Thus, the cleaning roller 41 can be rotated in the predetermined direction even when the motor 84 is rotated in the reverse direction.
In this way, the drive force of the motor 84 can be transmitted to the cleaning roller 41 by way of a switching operation of the swinging gear 92 to switch a transmission route of the drive force from the motor 84 to the cleaning roller 41. Thus, the cleaning roller 41 can be rotated in the predetermined direction irrespective of the rotating direction of the motor 84.